1. Technical Field
In general, this invention relates to battery chargers, and more particularly to a method of charging a secondary battery or string of batteries by the use of pulses of direct current, as opposed to continuous current, specifically where a repeated step in enactment of the method involves pulsed discharges of current taken from the battery or batteries string, interspersing such discharging pulses between charging pulses. Another aspect of general pertinence concerns timely switching back and forth between parallel aud series arrangements of circuitry. Types of batteries chargeable in accordance with the method to be described may include, but are not confined to, batteries having magnetized current collectors, such as those described in U.S. Pat. No. 6,194,093 B1 by O""Brien, the same inventor as at present.
2. Description of Related Art
Descriptions of battery chargers delivering charging current pulses interspersed by pulsed battery discharges are extant, including chargers devised to procure depolarization of batteries by means of the discharges. Such depolarization mitigates adverse consequences of high current rapid charging, including elevated internal energy losses, overheating, and gas evolution dangerously building up pressure within battery casings. In background discussion for U.S. Pat. No. 4,829,225 by Podrazhansky et al., earlier implementation of a reversedly pulsing approach to battery charging was credited to others, eg., Burkett et al.
U.S. Pat. No. 4,829,225 particularly teaches xe2x80x9ccharging a battery by providing a charge pulse to the battery, followed immediately by a depolarization pulse created by allowing the battery to discharge across a load, followed by a stabilization period, and repeating this sequence cyclically until the battery is charged.xe2x80x9d The same patent also suggests that the xe2x80x9cdischarge load may be provided by a transistor . . . controlled by the system control logic . . . to provide a variable resistance.xe2x80x9d There is ill suggestion by Podrazhansky et al. that the component loaded by discharge pulses should be a supercapacitorxe2x80x94preferably employing the new supercapacitors with magnetized parts that O""Brien describes in U.S. Pat. No. 6,556,424 B2 which is herewith incorporated by reference.
In general, one kind of distinction thought helpful for distinguishing between the reversedly pulsing (charging/discharging) arrangements of some inventions in this field, from others, is the distinction concerning the specific type of component or locally grouped set of components to which discharge pulses from a battery or, batteries string are to be delivered. Thus, on the point that discharges are delivered to a variable-resistance transistor for the Podrazhansky et al battery charger, more of a family resemblance thereto than strong distinction therefrom is perceptible in the pulsed charger described in U.S. Pat. No. 5,621,297 by Feldstein, who discloses means whereby discharge pulses flow through xe2x80x9cisolation diodesxe2x80x9d to xe2x80x9cdischarge current resistorsxe2x80x9d, as and when permitted by transistorized control. Podrazhansky et al and Feldstein therefore would likely concur in accepting the inevitable energy losses associated with delivering battery current to resistors. Acceptance of degradation of electric energy to heat is not part of the approach adopted for the present invention, however, albeit also involves interspersal of battery current discharge pulses between battery charging pulses.
Another approach perceptible in the background art is to locally group inductors and ordinary capacitors in suitably switched circuitry, so as to use a subset of inductors and capacitors both to discharge pulses of charging current into a battery or batteries string, and to intermittently receive pulses of battery current discharged thereto. This approach seems to use inductors and capacitors, basically, in substitution for the kind of use of resistors as has been mentioned above with regard to the Podrazhansky et al and Feldstein inventions. Both W. Newman in U.S. Pat. No. 4,016,473 and Pascual et al in U.S. Pat. No. 5,710,504 describe using inductors and capacitors grouped to intermittently receive delivery of battery discharge pulses.
When current flowing through an inductor is switched off, there will of course occur a collapsing magnetic field, causing dissipation of heat in local conductors, which is as truly an instance of energy degradation as is that occurring with components more ostensibly identified as resistors. The difference that resistors generate heat during the period of time when current is flowing, whereas inductors generate heat immediately after flowing current is interrupted, is not of significance to the point presently made, that the substitution for resistors that appears adopted by Newman and by Pascual et al incurs energy loss because of switching off inductors. Moreover, neither Newman nor Pascual et al specify a requirement that the capacitors they use to both transmit and receive pulsed current should be supercapacitors, as specified hereinafter as an essential feature of the present invention.
The abovecited Pascual et al. invention, which does not in every embodiment require using inductors to the same extent Newman uses them, is ostensibly concerned with art xe2x80x9cactive equalizationxe2x80x9d method whereby batteries in a long string way be equalized. The inference is not avoidable, however, that an incidental effect of the method of equalization proposed by Pascual et al. is depolarization procured in a substantially similar manner as for the several battery charger patents of the background art.
The practice of discharging depolarization pulses from a battery by use of a special charger is applicable to secondary electrochemical cells of well known types having solid-phase electroactive materials for anodes and cathodes, in contact with liquid-phase, usually aqueous, electrolyte solutions, noting that such cells operate at temperatures below melting points of the electroactive materials involved. High temperature cells using electroactive materials such as sodium and sulfur in a molten flowing state do not incur the identical entire set of problems addressed by pulsed charging methods, including, for example, the battery life cycle problem of shedding of electroactive materials from typical metal electrode grids or current collectors, which can occur due to the difference in thermal expansion properties between the grids and/or current collectors on the one hand, and the electroactive materials on the other hand. The present invention applies to the same types of batteries as do the background art inventions, and like them helps prolong battery life cycles by avoiding the high continuous current method of charging that exacerbates a tendency of overheated electrode assemblies to shed electroactive materials.
Objects of this invention include providing an improved method and apparatus for rapidly charging an electrically rechargeable battery or batteries string by a series of charging pulses, interspersed with battery discharge pulses effective to eliminate undesired concentration polarization, by substantially thinning or dispelling electrical double layers and diffusion layers at electrodes contacted by an aqueous electrolyte solution. Concurrent objects include prevention of overheating batteries, and of dangerously built-up pressure from gas evolution. A major general aim is to conserve energy in the course of enacting intermittent discharge pulses interspersed with charging pulses. An important specific object of invention is to effect discharge pulses in such a manner that electrical energy is not degraded to heat energy either by dissipation in resistive elements or in consequence of magnetic field collapses when local currents suddenly cease. Electrical energy of discharge pulses is to be stored temporarily in supercapacitors that will experience no significant heating during their service in accordance with the method of the invention.
For a preferred embodiment of the invention, the new supercapacitors with magnetized parts shall be employed to advantage; however, supercapacitors such as those to which the recent invention of supercapacitors with magnetized parts applies as an improvement will be serviceable in other embodiments, without necessity of magnetized parts. Regarding the preferred embodiment, permanent magnet materials for the pertinent parts will have been pre-selected for ability to withstand predetermined electrical conditions and current-associated magnetic fields, without incurring de-magnetization. A preferred embodiment charger, moreover, is expected to be most effective when the type of battery charged is one having magnetized current collectors.
Intermittent charging and discharging of electronic components is to be performed for three basic sections or subassemblies of grouped features, nominally referred to respectively using the terms xe2x80x9cfirst stagexe2x80x9d, xe2x80x9csecond stagexe2x80x9d, and xe2x80x9cthird stagexe2x80x9d, where the key feature of the third stage is a temporarily emplaced actual battery or batteries string to be brought up to full charge according to the method of the invention, and where the key feature of the first stage is a supercapacitor with a per discharge releasable capacity that may be scaled in typical instances at from about 10% to 25% of the total amount of energy stored by the end of the process in both the second and third stages. The first stage super-capacitor is charged by current from any suitable DC current source, such as a rectifier drawing mains AC current, or a generator.
The abovestated limitation pertaining to capacity of the first stage supercapacitor logically suggests needing from at least four to ten charging/discharging cycles of the first stage supercapacitor, to enact a typical complete battery charging process very rapidly. Actual practice would not necessarily be limited to a particular number of first stage discharges, however, because of variables in sizes and types of battery strings, aid rising costs of larger size supercapacitors, the pseudo-capacitance procuring materials in which are quite expensive.
Multiple surges of current to be periodically discharged from a first stage super-capacitor will be delivered into and through the array of second stage supercapacitors wherein they are alternately electrically connectable amongst one another in either a series or else parallel arrangement, besides being connected alternately in series or in parallel to the third stage, which in its instance when several batteries are stringed is also variably internally connected with the batteries in series or parallel, wholly or partially. Second stage super-capacitors should have higher energy storage capacities when batteries requiring relatively more protection from large charging surges are charged, and may have relatively lower capacities when not so much surge protection is needed by a particular battery type. An estimated 10% to 50% of the amount of energy the third stage (battery or batteries string) will ultimately store may be a suitable second stage capacity, but again the size and capacity for supercapacitors in the second stage may in practice vary for a number of reasons. It is generally desirable that there should be a possibility, at conclusion of the process, of storing energy in the second stage supercapacitors array. For example, assuming enactment of a complete battery charging procedure that involves ten discharges of a first stage supercapacitor, the last depolarization pulse of energy back to the second stage supercapacitors array from the third stage batteries string may be left stored in the second stage supercapacitors array for future use of any kind, including delivery in a manner to be described hereinafter to a load that may be the same electric motor the charged-up batteries are to power.
Regarding series and parallel arrangement alternatives amongst the second stage supercapacitors, they will have been electrically connected to one another in series, and in series to the third stage batteries also in series, just prior to receiving a surge of energy discharged from the first stage supercapacitor, the surge feeding both into the second stage supercapacitors array and a portion thereof passing therethrough to the third stage. The slope of the energy surge from a first stage discharge should be detected by a suitable sensor, used to ascertain when the surge subsides from peak energy transfer.
Charging pulse surge slope information should be fed to a microprocessor control unit responsible for switching electrical connections from series to parallel arrangements. At the same time the arrayed supercapacitors are in parallel with one another, a third stage batteries string may have some rather than necessarily all its batteries changed from series to parallel interconnection, depending on how close to completion is the overall charging procedure. During the initial and peak transfer phase of energy discharged by each pulse from the first stage supercapacitor, the second stage supercapacitors array operates in a filtering or smoothing mariner, so to speak, which protects the third stage batteries from deleterious consequences of a sudden power surge, such as overheating and damage to electrode structure which could otherwise occur from a similarly strong surge but absent the intervening second stage super-capacitors. During the lattermost portion of energy transfer from a particular discharge of the first stage supercapacitor, parallel interconnecting arrangements can procure an equalizing effect and reasonable speed and voltage of charging of the batteries.
Upon virtual exhaustion of a discharge from the first stage supercapacitor, this will be sensed by a suitable sensor and a switch will operate to disconnect the first stage from the remaining-connected second and third stages. During the period of its disconnection from them is when the first stage supercapacitor will be recharged from the DC source, and while this is happening a portion of the energy already received by the third stage batteries will be pulsed back into the second stage supercapacitors array in generally a similar manner as for the known depolarizing pulses in abovecited background art inventionxe2x80x94with the notable exception that here the so-called xe2x80x9cbucking voltagexe2x80x9d energy definitely is not dissipated in heat-generating components like resistors and/or inductors, because it will be received and conserved in the supercapacitors which are the special technical feature of the second stage.
During the periods of discharging a pulse of current to the second stage array of supercapacitors from the third stage batteries, as many of the letter as are needed to be in a series mode of arrangement should be switched thereto, in order that the voltage for their discharge pulse will be well above any voltage possibly remaining at the time in the second stage supercapacitors array, which itself should briefly be left in parallel arrangement for this period of reversed discharging, which is estimated to take typically from about 10 to 15 seconds. The time needed depends on how long it takes both for electrical double layers at the battery and supercapacitor electrodes, and for the diffusion layers adjacent battery and supercapacitor electrodes, to be dispelled, thereby, in the instance of the batteries, removing the principal causes of concentration polarization.
In the instance of the supercapacitors, reducing the time constant is effectedxe2x80x94in both instances, of magnetically enhanced batteries and magnetically enhanced supercapacitors, reducing internal resistance and preventing overheating and gas evolution. Time for dispelling diffusion layers, which is the slower attained of the two objectives here, since electrical double layers dispel more rapidly, is significantly shorter when magnetohydrodynamic stirring of an electrolyte solution is a present factor. The best contemplated way to match a shortened depolarizing discharge pulse period from the batteries is to employ supercapacitors in the second stage array which themselves feature a magnetically enhanced electrolyte convection process, by virtue of their having magnetized parts in accordance with the above cross-referenced related application, descriptive contents of which are properly incorporated herewith by reference.
Any suitable sensing means whereby a determination can be made that the diffusion layers adjacent battery electrodes have been dispelled will inform the microprocessor control unit of the fact, so that appropriate terminal reconnections readying the second stage for receipt of the next discharge pulse from the first stage supercapacitor may be made. By way of summary: while the depolarizing discharge pulse transfer of energy to the second stage array of supercapacitors from the third stage batteries takes place, the first stage supercapacitor is being brought up to its full charge state to ready it for discharge when connected again to the second stage. That re-connection should not occur until the second stage supercapacitors have been brought back again into series arrangement amongst themselves, which is best for absorbing the initial and peak transfer of energy to and through them. Their switching back to series may be initiated upon receipt of a microprocessor control unit of sensed information that a suitable amount of discharged current from the third stage say be inferred to have resulted in adequate battery depolarization for the time being.
Especially in view of extensive applicable details and options taught in prior art teachings of pulsed charging methods wherein it has been known to interperse discharge pulses from batteries, with charging pulses, now, together with a high level of skill and knowledge in the field, plus relatively recent disclosures by R. N. O""Brien (the present inventor) concerning magnetohydrodynamic stirring to reduce internal resistances of batteries and supercapacitors, it is considered instantly within the capabilities of artisans of the field, without need for undue experiment or necessity to independently discover special materials, to give engineered effect to the here-suggested present invention. For greater understanding of the suggestion, illustration by way of detailed description with reference to a schematic figure follows.